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Operational use of Primary and Secondary Channel

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Operational use of Primary and Secondary Channel

Old 29th May 2020, 02:12
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Operational use of Primary and Secondary Channel

Hello, I am new to this forum, I am an engineer working for a project to support VHF comms for aircrafts. I would like to clarify the operational use of primary and secondary VHF channels. I understand that the primary channel is used for ATC, what is the usage of the secondary? Only as a backup?
Thanks to anyone willing to answer
Luca Simonini is offline  
Old 29th May 2020, 23:33
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In my company, and most Iíve flown in, 121.5 unless operationally required to be on another frequency. This would normally only be for Parallel runway Approaches, calls to the company/ground handlers, and in Australia, we have some airports without ATC, so then we use the 2nd VHF for the local traffic frequency (CTAF).

Hope that helps
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Old 30th May 2020, 07:41
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I use mine to tune into ATIS broadcasts or to contact a second enroute airfield where necessary. I’ve also used it to contact handling agents.

I would think most others do similar.
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Old 30th May 2020, 07:55
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VHF 1 is usually used for "primary" communications with ATC. On many aircraft, the VHF 1 box is kept alive - for example by battery - when the aircraft electrical system is compromised. So it makes sense to use VHF 1 for primary ATC comms rather than having to switch boxes and frequencies in the event of electrical failure.

VHF 2 is used as a back-up for VHF 1 in the event of failure, and also for "house keeping" functions such as talking to handling agents, obtaining weather, talking to company operations, and in some cases - for example Gibralter - contacting the destination ATC to obtain approach clearance, while VHF 1 is tuned to an en-route ATC agency.

Thank you Denti, (below). I forgot to mention monitoring guard on VHF 2 Oops!

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Old 30th May 2020, 18:41
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Pretty much the same around the industry i guess.

VHF 1 is for ATC, VHF 2 usually kept on guard listening watch, and can be used operationally for weather, ops and the like if those are not reachable via datalink. VHF 3 is on datalink and not usually used for voice comm.

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Old 31st May 2020, 11:15
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Also in many parts of the world box 2 is needed for inflight broadcast procedures and negotiating entry at FIR boundaries, so ATC functions in addition to monitoring guard and house keeping stuff.
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